Field
The present disclosure relates to a fuel cell system and a method for discharging a fluid in the system.
Background Art
In the process of generating power, an impurity, such as nitrogen or carbon monoxide, or water accumulates inside a fuel cell system or a circulation flow path of a fuel off-gas. In order to discharge the impurities or water to the outside, a technique known as a purge technique has been used, in which an exhaust and drain valve is provided in a drain flow path connected to a circulation flow path, and the opening/closing of the exhaust and drain valve is controlled so as to discharge gases or water in the circulation flow path at each predetermined time.
Further, in order to secure the startup performance of a fuel cell system in a subfreezing environment, preventive measures have been taken to discharge the water or the like accumulated in a flow path on an anode side through an exhaust and drain valve by making use of a pressure difference immediately before the temperature of a component (e.g. the foregoing exhaust and drain valve) constituting the fuel cell system reaches zero degrees Celsius (see, for example, JP2007-305563A).
However, there is a case where, although the water around the exhaust and drain valve is discharged by making use of a pressure difference as described above, the water still remains on the side of a fuel cell stack, so that the water flows out from the fuel cell stack at the time of exhaust, causing inadequate drainage around the exhaust and drain valve. The inadequate drainage treatment poses a problem that, for example, the remaining water freezes in a subfreezing environment, causing a failure to secure the startup performance.